Conventionally, there are known construction machines including a machine body, an attachment mounted on the machine body pivotally around a horizontal axis, and a pipe supporting device for supporting a hydraulic pipe provided on the attachment.
For example, a pipe supporting device disclosed in Japanese Patent Publication No. 4704888 (hereinafter referred to as “Patent Literature 1”) includes a plate connected with an upper surface of an arm of a hydraulic excavator by welding, and a pipe clamp provided on the plate.
FIGS. 11 and 12 illustrate a state of the arm and the plate connected with each other by welding as disclosed in Patent Literature 1.
As shown in FIG. 11, the plate 21 is connected with an upper surface of a top plate 20 of the arm by fillet welding. Specifically, the plate 21 is connected to the top plate 20 by means of a weld bead 22 provided along mutually adjacent side surfaces 21a and 21b, as shown in FIG. 12. The side surfaces 21a and 21b of the plate 21 join each other at an angle 21c greater than 90 degrees, i.e. at an obtuse angle.
When the arm is operated, a stress occurs in the top plate 20 of the arm in a direction along the length of the arm (hereinafter, the direction of the stress will be referred to as a first stress direction D7). On the other hand, another stress may occur in the top plate of the arm in a second stress direction D8 perpendicularly intersecting the first stress direction D7 due to a reaction force received from a cylinder for driving a bucket when the arm is operated.
Here, the side surface 21a of the plate 21 extends in the first stress direction D7, i.e. in the direction perpendicularly intersecting the second stress direction D8. Therefore, the strength of the weld formed at the side surface 21a is liable to be insufficient against the stress occurring in the second stress direction D8.
Further, stress concentration is liable to occur at the weld formed at the corner between the side surfaces 21a and 21b. Therefore, the strength of the weld formed at the corner is also liable to be insufficient.
On the other hand, the side surface 21b of the plate 21 extends obliquely to both of the stress directions D7 and D8. This makes, among stress components acting in the stress directions D7 and D8, the stress component acting in a direction perpendicularly intersecting the side surface 21b smaller. Therefore, the strength of the weld formed at the side surface 21b is greater than that at the other part.
For the reasons described above, it is necessary to grind a perpendicular portion 22a (the hatched portion in FIG. 12) and a corner portion 22c (the cross-hatched portion in FIG. 12) of the bead 22 by a grinder G in order to improve the weld strength of the perpendicular portion 22 provided along the side surface 21a and the corner portion 22c provided along the corner.
Specifically, as shown in FIG. 11, the bead 22 is ground from a toe of weld of the bead 22 (perpendicular portion 22a and the corner portion 22c) over a predetermined region level so that the cross-sectional area of the bead 22 gradually increases in the second stress direction D8.
In this case, as shown in FIG. 12, the grinder G is caused to reciprocate in a grinding direction D5 parallel to the second stress direction D8 while moving in a movement direction D6 extending along the perpendicular portion 22a, to thereby grind the perpendicular portion 22a and the corner portion 22c. 
On the other hand, because the strength of the weld formed at the side surface 21b extending obliquely to both of the stress directions D7 and D8 is greater than that at each of the perpendicular portion 22a and the corner portion 22c as mentioned above, grinding of the oblique portion 22b of the bead 22 provided along the side surface 21b is omitted.
Therefore, the grinding using the grinder G is performed from the perpendicular portion 22a to a terminating end 23c defined by a boundary between the corner portion 22c and the oblique portion 22b. 
At this time, if a step is formed between the corner portion 22c and the oblique portion 22b at the terminating end 23c, stress concentration will occur thereat. In order to prevent this situation, it is necessary to perform a finishing treatment on the terminating end 23c so that the corner portion 22c and the oblique portion 22b join each other at the terminating end 23c smoothly in the second stress direction D8.
However, in the plate 21 disclosed in Patent Literature 1, the side surfaces 21a and 21b join each other at the obtuse angle. Therefore, when the grinder G is moved in the grinding direction D5 in order to perform the finishing treatment on the terminating end 23c, the grinder G is liable to come into contact with the side surface 21b located in the middle of the path of movement in the grinding direction D5, as shown by the reference numeral P in FIG. 12.
This makes it difficult to perform the finishing treatment on the terminating end 23c of the grinding.